This invention relates generally to methods and compositions for modifying the permeability of subterranean formations. In particular, this invention relates to methods and compositions for selectively pre-emptively mitigating unwanted water production prior to its occurrence in oil and gas wells.
Production of water and aqueous fluids from oil and gas wells is a common phenomenon which poses a variety of problems. For example, water production typically reduces the amount of oil and/or gas that may be ultimately recovered from a well since the water takes the place of other fluids that may flow or be lifted from the well. Thus, water production from oil and gas wells causes significant economic drawbacks. High water rates cause a reduction in well productivity and increase in operating expenditures. Furthermore, operating costs associated with disposal of produced water in an environmentally safe manner typically increase with the volume of produced water, thus increasing the threshold amount of hydrocarbons that must be produced in order to continue economical production of the well.
U.S. Pat. No. 6,228,812, which is incorporated herein in its entirety, discloses a chemical treatment that selectively reduces water production. Such treatments employ relative permeability modifiers (RPMs). The use of RPMs offers several advantages. For instance, the use of RPMs reduces costs since the chemicals are used in limited quantities and treatment does not typically require zonal isolation. In addition, the use of RPMs entails low risk since the polymer reduces the water permeability without adversely affecting oil permeability. Further, RPMs are simple to apply and do not require expensive equipment, such as rigs, for their application. It has been observed that suitable RPMs for such chemical treatment applications are homopolymers and copolymers of acrylamide, optionally having been sulfonated or quaternized, polyvinylalcohol, polysiloxane, or a hydrophilic polymer selected from natural gums and chemically modified derivatives thereof.
U.S. patent application Ser. No. 10/386,160, which is incorporated herein in its entirety, also discloses chemical treatment compositions useful for selective permeability modification of subterranean formations. The treatment employs RPM polymers capable of impeding the production of water and an organosilicon compound, the combination acting to substantially reduce the production of water in an oil or gas well without substantially affecting the production of hydrocarbons. The organosilicon compound is believed to attach to the RPM polymer as well as to the mineral surfaces of the formation, thereby increasing flow resistance and extending the effective RPM permeability application range.
Prior art applications of RPMs, as well as RPMs in conjunction with organosilicon compounds, are as water control treatment fluids which may optionally be used as a stimulation fluid. Accordingly, the water control treatment fluids are introduced into the subterranean formation prior to, together with, or following a hydraulic fracturing or other chemical well stimulation treatments. These prior art methods and compositions are relatively non-damaging to oil or gas permeability; for example, in oil saturated sandstone while exhibiting the ability to decrease water permeability substantially in water saturated zones. Therefore, the treatment compositions may be applied successfully to a production zone without the necessity of mechanical isolation in the wellbore, which can add significant costs to a water control treatment.
Although injecting treatment fluids containing RPMs has been effective for controlling unwanted water production, these techniques have been utilized after the problem has occurred. What is needed is a composition and a method for pre-emptively addressing anticipated unwanted water production prior to the occurrence.